The current invention relates to a health protecting apparatus for use during sunbathing. It involves the provision of a specially constituted thermoplastic screen offering both shade from the acute and chronic health damaging effects of intense visible and infra-red light, as well as the dangerous invisible short-wave ultra-violet light. At the same time however, the apparatus will permit safe sun-tanning by the transmitted long-wave ultra-violet light. The screen is constituted so as to exclude from the sunbather, by absorption, the major portions of dangerous erythematous and genotoxic solar radiations, (i.e. short-wave ultra-violet light, UV-B,intense visible white light, and infra red, I.R. wavelengths) at the time of exposure to the natural sun's rays which reach the earth's surface.
Many varied attemps have been made previously to formulate and construct a genuinely safe sun-screen but these have been generally ineffective because at best they only remove the dangerous short wave UV-B either by employing chemical absorbers (e.g. Gallowhur U.S. Pat. No. 2,391,959; Solvay et Cie, French Pat. No. 2236195), by mechanical processing of thermoplastic resins or yarns so as to impart UV-B filtering characteristics (e.g. Solvay et Cie British Pats. Nos. 1540568 and 1580975) or by including ground glass particles in the support resin and providing multiple spatially arranged laminates each with unique but additive absorption characteristics (e.g. Mutzhas British Pats. Nos. 1586687 and 1567979, and U.S. Pat. No. 4,200,360).
However, no previous attempts have been made to remove or reduce all three categories of dangerous light which it now seems (see infra) can interact synergistically to represent a very serious cosmetic and health threatening environment to man.
Recognition of the health hazard of UV-radiation has already prompted the U.S. Department of Health Education and Welfare (via NIOSH) to recommend occupational exposure limits to UV radiation including that of natural sunlight (HSM Pub. No. 73-11009) and there have also been calls by general medical practitioners for stricter controls on UV-parlors (Hawk, 1983; Retsas,1983). Also, a recent U.S. Bureau of Food and Drug Administration advisory panel recommended after reviewing available topical sunscreens: "Over-exposure to the sun may lead to premature ageing of the skin and skin cancer. The liberal and regular use of this product may reduce the chance of premature ageing of the skin and skin cancer".
In addition, apparently successful glass filters have been made and used for, in compliance with for example NIOSH, eye protection from the very dangerous far ultra-violet rays (UV-C) artificially produced by electric carbon arc welding equipment. These glasses employ total UV blockers such as the soluble green dyestuff "Filter-Blaugrun" (British Pat. No. 1060780) and are totally unsuitable for sunbathing because they block the harmless UV-A light as well as eye-sight damaging UV-B and UV-C.
The disadvantages of these earlier screens are that they are either prohibitively expensive to produce, protect the sunbather from only UV-B sunburning rays and not from the overheating or IR-burning rays, or that they block out all the UV-light and prevent tanning altogether. None of the prior art products protect the sunbather from dangerous intense visible or infra-red light which is now thought to be potentially as dangerous as UV-B with respect to cancer induction and skin ageing (see infra).
Terrestrial sunlight has been considered to consist of, with very slight variations of definition, short-wave ultra-violet light (UV-B, 290-320 nm), long-wave ultra-violet light (UV-A: 320-400 nm), visible light (400-700 nm) and infra-red light (wave-lengths ranging from 700-15,000 nm. On a clear day at sea level, the distribution of solar radiation is about 1-2% UV, about 42% visible light and about 57% infra-red. At higher altitudes, at any given latitude, the amount of solar radiation available, especially UV, is increased so much that at the highest altitudes, at sub-zero temperatures a climber needs very effective sunburn protection.
It is now generally recognised that UV-B is dangerous to health and excessive natural exposure can lead to sun-burn (erythema), skin ageing and cancer. UV-A is apparently harmless at natural intensities and induces skin tanning. Visible or white-light has also been considered safe, although there are now reports that there are some disorders of the skin, particularly those involving photosensitivity reactions, skin ageing and cancers, which can occur in those individuals exposed to intense light. The most serious commonly occuring hazards of excessive exposure to visible and infra-red light involve dehydration due to over-heating, ultimately leading to unconsciousness, sunstroke and even death.
Current literature surveys confirm that the deleterious rays of the sun are in the UV region (Cleaver, 1970), and the sun-burning rays (UV-B) are carcinogenic (Blum, 1959, Magnus 1976 and Forbes et al 1978). UV-A on the other hand requires vastly higher exposure doses than UV-B to produce only benign papillomas (Forbes et al 1982).
Sunlight extends of course from the UV-region into the regions of visible light, infra-red and ultimately radio waves. The latter can probably be disregarded with respect to dermal effects, but visible radiation cannot (Kligman & Kligman 1984). Harmful effects such as phototoxic reactions (Kaidby & Kligman 1978) through DNA cross-linking (Gantt et al 1979) to tumor enhancement (Griffin et al 1955) have been recorded. Visible light also causes solar urticaria in some people (Harber & Bichers, 1981).
The precancers and cancers resulting from UV irradiation are now well recognised, but the fact that acute heat exposure can also cause squamous cell carcinomas (Lawrence 1952) is insufficiently well appreciated, as is the fact that chronic heat exposure in the physiological range can result in neoplasm induction. Evidence for these effects are derived from China (Kang cancers), India (Kangri cancers of Kashmir), Japan (Kairo cancer), Ireland (Turf or Peat Fire Cancer), and Australia (epithelioma due to spectacles focussing IR radiation on the cheeks) (See Kligman & Kligman 1984). The similarities between IR and UV induced skin cancers are strikingly obvious (Kligman 1969). In addition, it seems that skin ageing (elastosis and the like), erythema ab igne, and cancers, can be produced by either route and indeed there is a distinct probability that enhancement of chronic actinic damage by IR radiation is of great importance in the etiology of human cancers (Kligman 1982). Clearly, whenever isolation is high, heat is a concomitant factor and sunbathing in the midday sun entails being irradiated by the far from innocuous UV-B and IR rays. The sunscreen formulation described below contains materials arranged so that both heat and UV-B are deflected away from the bather while simultaneously reducing glare by absorption and diffusion of the UV-A and white light.
At present, in order to avoid unpleasant sun-burning and genotoxic effects, premature ageing, solar keratoses, or induced malignant neoplasms, a person who relaxes or is active in strong sunshine is obliged to shield his or her skin from the sun. Such shielding can be effected by the wearing of clothing overall, but this often is not desirable, or even practicable, depending upon the activity being pursued, especially since strong sunshine is usually associated with high temperatures. If the person wishes to be relatively unclothed it is usual to apply creams,lotions or the like to the exposed parts of the body, such substances containing ingredients which purport to absorb some at least of the sun's UV-B, and in some cases UV-A, radiation and thereby prevent or reduce the incidence of the above effects of solarisation. If a person wishes to remain exposed to the sun's radiation for a long period of time, to achieve a suntan for example, frequent and liberal re-application of the cream or lotion is required, which is inconvenient, costly and may itself be a dangerous practice (Lane-Brown et al 1980). Even so, protection from IR either as a direct heating agent or as a cancer inducing agent, or protection from eye-strain, glare, or conjunctivitis, virus activation such as Herpes, dehydration, headache, and the like is of course not provided for by such lotions, and the sunbather is sooner or later obliged to retire from exposure to the sun through heat exhaustion, semi-blindness, and/or by good sense.
As an alternative it may be possible to relax or perform the activity under a roof, canopy or the like which is rendered transparent or translucent to the safe suntanning UV-A radiation but which absorbs the sun's dangerous UV-B and a biologically significant proportion of the sun's visible and IR radiation so as to prevent or reduce the above undesirable effects whilst, at the same time, to permit the desirable effects of shade and tanning.
The beneficial effects of sunlight should not be overlooked. Effects which have been known for many years, e.g. heliotherapy has been used for prophylaxis and treatment of rickets, the synthesis of vitamin D, secondary aneamia, various types of tuberculosis, and skin infections. A deep-seated relation is known to exist between skin tanning and the sex hormone system in males (Hamilton and Herbert 1938) and in females (Hamilton, 1939).
The problem to date has been how to achieve safe and beneficial sunbathing with exclusion of insidious acute and chronic effects.
Most known unpigmented light transparent materials, e.g. glass, quartz, or various types of plastic sheeting, transmit most, if not all, of the sun's dangerous radiation and are, therefore, not suitable for the production of sunscreens since they do not preclude either actinic burning of, dazzle or glare from, heat absorption by, or any chronic synergistic effects in anyone remaining shielded from the sun by such means.
Such materials are used in the construction of so called "sun lamps" and "sun beds". In this case, however, the lamps associated with the equipment are such as to provide only the safe UV-A wavelength range of radiation to produce the tanning effect without burning, and they rely heavily on forced air circulation or heat sinks to provide cooling and heat dissipation. Nevertheless contamination of the emitted UV-A with UV-B is now considered to be a serious deficiency and a potential health hazard to the user of such lamps (Degun et al 1982).